VINYL CYCLOHEXENE DIOXIDE

OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.

CAS: 106-87-6; Chemical Formula: C₈H₁₂O₂

OSHA had no former PEL for vinyl cyclohexene dioxide (VCD). OSHA proposed establishing a 10-ppm TWA PEL, with a skin notation, for VCD, and this limit is established in the final rule. NIOSH (Ex. 8-47, Table N6A) agrees that this limit is appropriate and notes its determination that VCD is a potential human carcinogen. The ACGIH classifies VCD as a suspected human carcinogen (A2). Vinyl cyclohexene dioxide is a colorless liquid used as a chemical intermediate and as a monomer in the manufacture of polyglycols containing unreacted epoxy groups (Hine, Rowe, White, Darmer, and Youngblood 1981/Ex. 1-976). It is also used as a reactive diluent for other diepoxides and certain epoxy resins (IARC 1976).

Turchi, Bonatti, Citti et al. (1981/Ex. 1-282) assayed the mutagenicity of VCD and several other epoxides using the TA100 strain of S. typhimurium and V79 Chinese hamster cells; these authors also investigated the alkylating properties of these chemicals. VCD tested positive in both the S. typhimurium test (point mutation) and the V79 Chinese hamster cell test (both point mutation and chromosome aberration), and had an intermediate alkylating capacity relative to other epoxide compounds tested.

There are no data concerning the adverse health effects of VCD in humans. There are no reports as a result of industrial experience that reveal carcinogenic effects in workers caused by VCD exposure (ACGIH 1986/Ex. 1-3).

Four studies have reported the development of skin tumors in mice exposed dermally to VCD (Hendry, Homer, and Rose 1951/Ex. 1-250; Kotin and Falk 1963/Ex. 1-287; Weil, Condra, Haun, and Streigel 1963/Ex. 1-257; and Van Duuren, Nelson, Orris, Palmes, and Schmitt 1963/Ex. 1-288). The study of Van Duuren et al. (1963/Ex. 1-288) included controls and is thus particularly well suited for an evaluation of VCD’s carcinogenic potential.

These authors painted 30 male Swiss ICR/Ha mice with 0.1 ml of a 10-percent solution of VCD in benzene three times per week (approximately 100 mg of solution per application). Two negative controls were used; one set of 150 mice was treated with benzene alone and another set of 207 mice was not treated with anything. Fourteen of the 30 VCD-treated mice developed skin tumors after an undefined length of time (mean survival time was 326 days). The incidences of skin tumors in the controls were 11/150 and 13/207 for the benzene-treated and untreated mice, respectively. The incidence of skin tumors in the VCD-treated mice was significantly greater than the incidence observed in either of the controls (Van Duuren, Nelson, Orris, Palmes, and Schmitt 1963/Ex. 1-288).

The study of Van Duuren et al. (1963/Ex. 1-288) demonstrates the carcinogenicity of VCD in experimental animals. OSHA considered the possibility of conducting a quantitative risk assessment for VCD, and the Agency concluded that the dose-response data in this study are unsuitable for quantitative risk assessment purposes because the VCD was administered in a solution of benzene, which is itself regulated as a carcinogen and classified as such by several authorities (IARC, NTP, NIOSH, and ACGIH). Even though the Van Duuren et al. (1963/Ex. 1-288) study included a control for the independent carcinogenic effects of benzene, the possibility of a synergistic or additive effect of benzene on VCD cannot be completely ruled out.

Vinyl cyclohexene dioxide has been shown to be carcinogenic by dermal application in mice, and four studies have confirmed these effects. Based on these animal studies showing VCD’s carcinogenicity, OSHA concludes that exposed employees are at significant risk of cancer potentially associated with exposure to VCD at the uncontrolled levels formerly permitted by the absence of an OSHA limit. The Agency considers this effect a material impairment of health. No comments, other than NIOSH’s, were received pertaining to VCD. The Agency concludes that promulgation of a 10-ppm 8-hour-TWA PEL, with a skin notation, will substantially reduce the significant occupational risk confronting VCD-exposed employees.